1. Field of the Invention The invention relates to pressure swing adsorption operations. More particularly, it relates to such operations under variable demand conditions.
2. Description of the Prior Art Pressure swing adsorption (PSA) processes and systems are well known in the art for achieving desirable separation of the components of a feed gas mixture. In the practice of the PSA process, a feed gas mixture containing a more readily adsorbable component and a less readily adsorbable component is passed to an adsorbent bed capable of selectively adsorbing the more readily adsorbable component at an upper adsorption pressure. The bed is thereafter depressurized to a lower desorption pressure for desorption of said more readily adsorbable component and its removal from said beds prior to the introduction of additional quantities of the feed gas mixture thereto as cyclic adsorption-desorption operations are continued in the PSA system. In conventional PSA practice, multi-bed systems are commonly employed, with each bed employing the PSA processing sequence on a cyclic basis interrelated to the carrying out of said sequence in the other beds of the system.
A highly advantageous application of the PSA technology relates to the separation of air to produce product nitrogen and co-product oxygen gas. For such operations, equilibrium type adsorbents, such as zeolite molecular sieves, are commonly employed and serve to selectively adsorb nitrogen as the more readily adsorbable component of air, while allowing oxygen to pass through the bed of adsorbent material as the less readily adsorbable component. A steady stream of nitrogen and oxygen of desired concentration can thus be produced.
While PSA processes and systems can readily be optimized for desired nitrogen and oxygen production under steady state conditions, the demand for such gaseous products does not remain constant over extended periods of time in various practical commercial applications. There is a need in the art for the development of PSA processes and systems suitable for operation under variable control conditions. Turndown control means are thus required so that the PSA systems can be operated efficiently so as to maintain desired product supply and purity under variable user demand conditions, while reducing power requirements under reduced demand conditions.
It is an object of the invention, therefore, to provide a PSA process and system for the production of nitrogen and oxygen from air under variable demand conditions.
It is another object of the invention to provide an improved PSA process and system for enhancing the efficiency of air separation operations under reduced nitrogen product gas conditions.
With these and other objects in mind, the invention is hereinafter described in detail, the novel features thereof being particularly pointed out in the appended claims.